ABSTRACT Treatment for bone deformities secondary to malunited fractures usually require corrective osteotomies, and high incidence of surgical failure rates have been reported. Inaccurate corrections and loss of reductions are among the most common causes, and these technical errors ought to be improved. A new measuring fixator for humeral supracondylar corrective osteotomies in children was designed and used in clinical application. Two boys who had sustained cubitus varus following malunited humeral supracondylar fracture were performed using proposed measuring fixator. The results of the clinical trial show that the angle of correction was accurate, and the procedure could be carried out by the surgeon himself without additional help, with an average of 1.3 penetration of the physis per each fixating Kirschner wire (8 times in 6 K-wires). The surgical time was reduced, as well as the radiation exposure.

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Reports of corrective procedures for cubitus varus (gunstock deformity) have emphasized the frequency of loss of position and significant complication. Modifications that have been made to the standard supracondylar osteotomy protocol include correction of the angular deformity only, without correction of rotation; an incomplete wedge osteotomy leaving the medial cortex intact by hinging the osteotomy shut on the intact cortex; and immobilization of the elbow in full extension with the forearm supinated. In a review of 16 patients following this protocol, 11 patients had excellent results, three had good results, and two had unsatisfactory results.

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Between 1970 and 1992, 23 patients with cubitus varus deformities following elbow fractures underwent 26 corrective lateral-wedge osteotomies at Texas Scottish Rite Hospital. Internal fixation was most commonly provided by either small Steinmann pins, two screws and a figure-of-eight wire, or a small two-hole plate. Sixteen patients had a good result and 10 were judged to have poor results. Two of the 10 patients with poor results had inadequate intraoperative correction. Unstable internal fixation allowed osteotomy fragments to slip into varus in the remaining eight poor results (three with Steinmann pins and five with figure-of-eight wire). Nonrigid internal fixation was obvious even in the patients who received good correction of their cubitus varus. Of the 16 patients with good postoperative results, six demonstrated loss of fixation with extension of the distal fragment. In addition, seven patients with poor results also had slippage of the distal osteotomy fragment into extension. These patients had between 5 and 15 degrees of apparent elbow hyperextension with concomitant loss of elbow fixation. We now recommend a two-hole lateral plate and a percutaneous medial pin to enhance the stability of internal fixation.

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From 1974 to 1986, a step-cut technique of distal humerus valgus osteotomy using one cortical screw for fixation was used to correct cubitus varus deformity in 11 patients. The results were graded as excellent, eight patients, good, two, and poor, one. The poor result was secondary to persistent varus. The average humeral-elbow-wrist angle in the ten patients with valgus correction roentgenographically measured 9.3 degrees. The average amount of correction was 28.4 degrees. All patients retained their preoperative level of elbow motion. There were no radial or ulnar nerve injuries, nonunions, infections, or hypertrophic scars. The osteotomy requires careful preoperative planning and special attention to surgical detail. Large amounts of deformity may be corrected safely with a low complication rate.

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BIOMEDICAL ENGINEERING-APPLICATIONS, BASIS & COMMUNICATIONS 27 A NEW MEASURING FIXATOR DESIGN FOR HUMERAL SUPRACONDYLAR CORRECTIVE OSTEOTOMIES IN CHILDREN SHUO-SUEI HUNG1, MING-YIH LEE2, CHIN-HSIUNG HSU2, WEN-DA TZAI , ZHON-LIAO LEE department of Orthopedic Surgery, Chang Gung Memorial Hospital and St. Paul's Hospital, 2Graduate Institute of Mechanical Engineering, Chang Gung University, department of Orthopedic Surgery, Chang Gung Memorial Hospital and Children's Hospital, Taoyuan, Taiwan ABSTRACT ABSTRACT Treatment for bone deformities secondary to malunited fractures usually require corrective osteotomies, and high incidence of surgical failure rates have been reported. Inaccurate corrections and loss of reductions are among the most common causes, and these technical errors ought to be improved[l-2]. A new measuring fixator for humeral supracondylar corrective osteotomies in chil-dren was designed and used in clinical application. Several surgical trials were performed in vitro using rapid prototype models to simulate different bony deformities. Two boys who had sustained cu-bitus varus following malunited humeral supracondylar fracture were performed using proposed measuring fixator. The results of the clinical trial show that the angle of correction was accurate, and the procedure could be carried out by the surgeon himself without additional help, with an average of 1.3 penetration of the physis per each fixating Kirschner wire (8 times in 6 K-wires). The surgical time was reduced, as well as the radiation exposure. time was reduced, as well as the radiation exposure. Biomed Eng Appl Basis Comm, 2003 (February); 15: 27-31. Keywords: Supracondylar corrective osteotomy, Measuring fixator, Surgical tool Keywords: Supracondylar corrective osteotomy, Measuring fixator, Surgical tool may also contribute in other situations. These pa-tients are clinically free of functional limitation, and often c o m e t0 he]p for c o s m e tjc purpose due to varus deformity of the elbows. There are seldom complaints of pain or weakness[8]. Several different surgical procedures have been developed in the past with variable results[ 1,8-10], and they all involve corrective osteotomies. The postopera-tive complications reported include nerve injury, bra-chial artery aneurysm, pin tract infection, elbow stiff-ness, or scarring[5). However, the most commonly en-countered is the recurrence of cubitus varus due to loss 0f correction, which could be as high as 46%, and the leading causes have been suspected being such as phy-seaj injuries or technical errors[ 1 -2]. To minimize such complications, every single step during the operation must be proceeded carefully. appropriate surgical tool, surgical procedures may be-1 HVTROniTf~"TTO?V 1. IN I mJLFUl^1 l\Jiy Cubitus varus is one of the most common compli- cation following humeral supracondylar fracture in children, and the incidences reported varies from 9% to 57% [3-5]. Some authors suggest that malunion with medial tilting of the distal fragment may be the main cause leading to this deformity, however, rotation of the distal fragment[6], as well as physeal injury[7], ■— ■ Received: Jan. 8,2003; Accept: Feb. 12, 2003 Correspondence: Ming-Yih Lee, Ph.D., Professor Department of Mechanical Engineering, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Tao-Yuan, Taiwan E-Mail: leemiy@mail.cgu.edu.tw However, without an - 27 Treatment for bone deformities secondary to malunited fractures usually require corrective osteotomies, and high incidence of surgical failure rates have been reported. Inaccurate corrections and loss of reductions are among the most common causes, and these technical errors ought to be improved[1-2]. A new measuring fixator for humeral supracondylar corrective osteotomies in chil-dren was designed and used in clinical application. Several surgical trials were performed in vitro using rapid prototype models to simulate different bony deformities. Two boys who had sustained cu-bitus varus following malunited humeral supracondylar fracture were performed using proposed measuring fixator. The results of the clinical trial show that the angle of correction was accurate, and the procedure could be carried out by the surgeon himself without additional help, with an average of 1.3 penetration of the physis per each fixating Kirschner wire (8 times in 6 K-wires). The surgical Biomed Eng Appl Basis Comm, 2003 (February); 15: 27-31.

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28 Vol. 15 No. 1 February 2003 come difficult and inaccurate In this paper, design of a handy measuring fixator for corrective osteotomy was reported, which will not only allow the surgeon to obtain an adequate angle of correction, but also serves as a temporary fixator to permit an easier and more accurate fixation of the os-teotomy site. Several rapid prototype models of elbow and hip deformities were used for in vitro trials of the device. Surgeries have been performed with this de-vice, and its clinical applicability is discussed. 2. MATERIALS AND METHODS The first step to a successful result during the sur-gery of valgus closing wedge osteotomy is to obtain an adequate angle of correction, which is usually difficult to determined and very often underestimated intraop-eratively. The second obstacle that a surgeon may en-counter is to maintain the position of bone fragments prior to fixation. In general, positioning reconfirmation under fluoroscope is required. To minimize the expo-sure to radiation, a- single lateral K-wire from the lat-eral condyle is usually applied to replace manual hold-ing of the fragment, and if the position is acceptable, additional one or two K-wires will be applied in situ, provided that the fragment has not rotated during this procedure while changing the images from anteropos-terior view to a lateral view. Otherwise, repositioning and reconfirmation will have to be repeated. Simi-larly, if the initial position is not appropriate, read-justment is necessary for the fragment, as well as the fixation of lateral K-wire, and multiple physeal pene-tration may have resulted. To confront the above-mentioned problems, a de-vice was designed in-house and intended to allow the surgeons, first of all, to achieve an accurate angle of osteotomy, and with the same device, to obtain a tem-porary stability of the fragments during fluoroscopic Fig. lA-View of the device when assembled with K-wired inserted over the two arms.lB-View of the device not in use when folded. evaluation before final fixation (patent pending). As shown in Fig. 1 A, this stainless steel measuring fixator comprises of a semicircular frame with a central slot, and two arms that slide along the slot with range of motion of 60 degrees of circumference (30° on each arm). These two arms are connected indirectly onto the bone through two K-wires, and can be used as joy-sticks for manipulation of the bone fragments. Higher dexterity in manipulation is designed in terms of rotation and translation between the two arms, to compensate with different surgical scenarios. This de-vice is durable, and can be reassembled to a fairly compact size during storage or autoclaving as shown in Fig. IB. This measuring fixator was designed using com-puter aided design / computer aided manufacture (CAD/CAM) technologies. With Solid Works® pack-age, each component of this device was created indi-vidually (Fig. 2A). After that, mechanical links were assembled together for kinematic simulation under the Working Model® software (Fig. 2B). In this studies, three different prototypes were designed, and the final device was decided through numerous modifications according to the surgeons opinions. 3. SURGICAL PROCEDURES The patient is placed in supine position under standard sterile draping and surgical exposure. After careful preoperative planning, the device is set at the necessary angle, and since there is a residual angle of 5 degrees formed by the two arms at the closest distance due to structural limitation, the same amount of ad-justment should be added initially to ensure an ade-quate correction angle (Fig. 3A). The device is then placed to the osteotomy site, and fixated through the two tunnels on each arm with K-wires. The device is then removed, leaving the K-wires oriented to the pre-planned cutting planes, which subsequently serve as guides for performing osteotomy (Fig. 3B). During surgery, bone resection is done with a small bone saw under well protection, and the device Fig. 2A-CAD design of the device by Solid Works®. 2B-Motion simulation of the device by Working Model® - 2 8 -

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BIOMEDICAL ENGINEERING-APPLICATIONS, BASIS & COMMUNICATIONSFig. 3A-The device is adjusted to the angle of os-teotomy, and Kirschner wires are inserted throughthe tunnels over each arm. 3B-The device is dis-mounted, leaving the Kirschner wires as guides forbone cutsFig. 4A-The device is repositioned onto the Kir-schner wires after osteotomy. 4B-The bone frage-ments are brought together by manipulating thearms, and fixation is performed.is mounted. back onto the K-wires. The bone fragmentsare approximated after releasing the locking knobs thatconnect the arms to the frame, and relocked at theproper position (Fig. 4A). The osteotomy site can bemaintained temporarily at a good stability for fluoro-scopic examination at this moment, and readjusted eas-ily by releasing the knobs, without reapplication of theK-wires (Fig. 4B). When the position of the fragmentsare reconfirmed, final fixations can be achieved withadditional crossed or parallel K-wires.4. RESULTSBefore clinical trial, we have performed two labo-ratory tests on the rapid prototyping models, one of thehip and the other one of the elbow, and also on a ca-daveric humeral bone with success. Two clinicalcases were carried out, and the clinical case presentedhere was a 5 year old boy who had sustained left elbowinjury about 3 years priorly, and cubitus varus resultedfollowing closed reduction and long arm casting. Hiscarry angle was 30 degrees varus over the lesion side,and 5 degrees valgus over the contralateral side, there-029Fig. 5A-Preoperative X-ray showing a varus carryangle. 5B-Postoperative X-ray film with multiple K-wire fixations.fore, the planned angle of correction was set to be 35degrees valgus. (Fig. 5A)Due to good stability obtained by the device, fixa-tion was performed easily without any help of addi-tional assistance (Fig. 6A-B). Three pieces of Kir-schner wires were used, and a total of four physealpenetrations were made on this patient's humeralcondyle.Intraoperative fluoroscopic evaluation wasperformed (Fig. 7). The postoperative anteroposteriorview is shown on figure 5B.5. DISCUSSIONSCorrective osteotomy is the only effective methodfor correction of established malunited fracture or bonedeformity[11-12]. Among the several methods of os-teotomies, valgus closing wedge is a simple and prom-ising choice for cubitus varus deformity followingmalunited humeral supracondylar fracture[ 1,13].Even with meticulous preoperative planning, sev-eral pitfalls must be overcome during the operation toensure a successful result. Precise osteotomy is one ofthe most critical influencing factors, and both lateralwedging and anteroposterior wedging must be takeninto account when performing such procedure. Loss ofreduction is another main cause of failure, and this canoccur either intraoperatively or postoperatively[ 14].Fixations are recommended as minimal as possible toavoid multiple penetrations of the cortex and physis,but rotation is inevitable with only a single K-wirefixation as the surgeon would usually apply, during theprocess of reconfirmation under fluoroscopy andevaluation for the gross elbow range of motion.Lastly, even during the final stage of fixation, eitherchosen to be with K-wires, screws, or even plates, lossof reduction is still possible without a suitable boneholder[15]. With proposed innovative measuring fixa-tor, the above mentioned problems can be solved eas--29-

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30 Vol. 15 No. 1 February 2003 Fig. 6A-Application of Kirschner wire fixation is feasible without additional assistance. 6B-View of the sur-gical field after fixation. ily, and the operation can be carried out efficiently with less radiation exposure to both the patients and the clinical staff. Several surgical tools have been developed for corrective osteotomies, however, they are mainly fo-cusing on the proximal tibia and femur[16-19], and scarcely over the humeral supracondyle. Application of computer assisted preoperative planning has been started for decades, and thorough discussions have been reported in other literatures[20-22]. The major advantages of using the CAD/CAM technologies lies on that not only can the design be modified easily, but also be tested virtually before being manufactured, which is both efficient and economic. After under-standing the needs of the surgeons, several different designs have been developed and modified. Finally, a novel measuring fixator was designed mainly focusing Fig. 7 Fluoroscopic reconfirmation of the osteot-omy. A single Kirschner wire on each arm was able to provide sufficient stability in this case. on the simplicity of the instrument, and the ease of ap-plication, as Coyler suggested in his literature for the proximal femoral osteotomy[23]. Rapid prototype models are initially used in the field of industry as an fast and simple method to obtain the physical shape of the designed model, and has re-cently been applied in the medical field in several ways. In this study, several trials were performed over the rapid prototyping models of humerus to famil-iar with the use of the device before performing on the clinical cases. It is found that these physical replica models are helpful not only in the way that the supply is unlimited, but different deformities can be accu-rately produced. In addition, a real osteotomy was performed on a piece of adult cadaveric humeral bone. Although this instrument was originally designed for use in the pediatric elbow, we experienced even a good stability on the adult bone. In addition to the proposed closing wedge osteot-omy, it is believed that this instrument is also suitable for opening wedge osteotomy, and the surgical site is not limited to the supracondylar area, but other lesion sites as well. Further applications of this device will be carried out in the future. 6. CONCLUSION Few devices have been reported in assistance for the humeral supracondylar osteotomy in children, yet such surgeries are not uncommon in daily practice for an orthpaedic surgeon. With the aid of computer CAD/CAM technology, an innovative measuring fixa-tor was designed and produced. Rapid prototyping technologies was applied to produce physical replica models of humerus for pre-operational reharsal. Two clinical trails was performed using proposed instru-ment with a positive results. This is another indica--30-